Method and an apparatus for recovering furfural

ABSTRACT

In a method and an apparatus furfural is recovered from a steam stream ( 3 ) which is formed in a treatment of a pretreated wood based material ( 1 ). The pretreated wood based material ( 1 ) which comprises at least carbohydrates is treated in a steam treatment stage ( 2 ) in which the steam is released. The steam stream ( 3 ) which comprises furfural is supplied out from the steam treatment stage ( 2 ). A pretreated and steam-treated wood based material ( 4 ) which comprises carbohydrates is supplied out from the steam treatment stage ( 2 ), and the steam stream ( 3 ) is treated in a recovery stage ( 12   a,    12   b ) for recovering a furfural based fraction ( 14   a,   14   b ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage of International ApplicationNo. PCT/FI2017/050930, filed Dec. 22, 2017, which claims the benefit ofFinnish Patent Application No. 20166049, filed Dec. 30, 2016, both ofwhich are hereby incorporated by reference in their entireties.

FIELD

The invention relates to a method and an apparatus for recoveringfurfural from a steam stream which is formed in a treatment of apretreated wood based material.

BACKGROUND

It is known different methods for forming carbohydrates and lignin fromdifferent raw materials, such as biomass. Many bio-refinery processes,e.g. a hydrolysis, generate lignin and sugars after the treatment of thebiomass. It is known that sugar streams comprise also other chemicalcompounds, e.g. furfural.

OBJECTIVE

The objective of the invention is to disclose a method for recoveringfurfural from wood based material. Another objective is to removefurfural from products and streams formed in the treatment of the woodbased material. Another objective is to separate furfural from the woodbased material.

SUMMARY

The method for recovering furfural is characterized by what is presentedin claim 1.

The apparatus for recovering furfural is characterized by what ispresented in claim 21.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and constitutes a part of thisspecification, illustrate some embodiments of the invention and togetherwith the description help to explain the principles of the invention. Inthe drawings:

FIG. 1 is a flow chart illustration of a method according to oneembodiment,

FIG. 2 is a flow chart illustration of a method according to anotherembodiment,

FIG. 3 is a flow chart illustration of a method according to anotherembodiment,

FIG. 4 is a flow chart illustration of a method according to anotherembodiment,

FIG. 5 is a flow chart illustration of a method according to anotherembodiment,

FIG. 6 is a flow chart illustration of a method according to anotherembodiment,

FIG. 7 is a flow chart illustration of a method according to anotherembodiment,

FIG. 8 is a flow chart illustration of a method according to anotherembodiment, and

FIG. 9 is a flow chart illustration of a method according to anotherembodiment.

DETAILED DESCRIPTION

In a method for recovering furfural from a steam stream (3) which isformed in a treatment of a pretreated wood based material (1), thepretreated wood based material (1) which comprises at leastcarbohydrates is treated in a steam treatment stage (2) in which thesteam is released, the steam stream (3) which comprises furfural issupplied out from the steam treatment stage (2), a pretreated andsteam-treated wood based material (4) which comprises carbohydrates issupplied out from the steam treatment stage (2), and the steam stream(3) is treated in a recovery stage (12 a, 12 b) for recovering afurfural based fraction (14 a,14 b).

One embodiment of the method is shown in FIG. 1. Another embodiments ofthe method are shown in FIGS. 2-9.

The apparatus for recovering furfural comprises at least one a steamtreatment stage (2) which comprises at least one steam treatment deviceand in which the pretreated wood based material (1) which comprises atleast carbohydrates is treated and in which the steam is released, atleast one discharge means, e.g. discharge device, for supplying thesteam stream (3) which comprises furfural out from the steam treatmentstage (2), at least one discharge means, e.g. discharge device, forsupplying a pretreated and steam-treated wood based material (4) whichcomprises carbohydrates out from the steam treatment stage (2), and atleast one recovery stage (12 a, 12 b) which comprises at least onerecovery device, for recovering a furfural based fraction (14 a,14 b)from the steam stream (3).

In this context, a steam stream (3) means any steam stream which isformed, e.g. by separating, collecting or recovering, from a pretreatedwood based material (1) in any steam treatment stage (2) and whichcomprises at least furfural. The steam stream (3) may comprise alsoorganic acids, such as acetic acid or other organic acids. The steamstream may comprise also other components, such as side and degradationproducts. In one embodiment, the steam stream (3) is a steam fraction ofthe pretreated wood based material. The steam stream (3) may be formedfrom the pretreated wood based material after any suitable steamtreatment stage, e.g. a steam explosion stage. The steam treatment stagecomprises at least one steam treatment device, such as steam explosiondevice. In one embodiment, the steam treatment stage (2) is a steamexplosion stage. In the steam explosion stage the pretreated wood basedmaterial (1) is treated by the steam explosion, in which hemicellulosesare treated and in which at least a part of polysaccharides of thehemicelluloses degrade into monosaccharides and oligosaccharides bymeans of a hydrolysis and in which pressure is rapidly released. In oneembodiment, the steam treatment stage (2) comprises at least oneseparation step or separation device, e.g. cyclone, in which the steamstream (3) and the pretreated and steam-treated wood based material (4)are separated. Preferably, the steam stream (3) is in the form of steamor vapor, e.g. water based steam. In one embodiment, temperature of thesteam stream is 90-110° C. after the steam treatment stage (2).

In one embodiment, the pretreated wood based material (1) comprises atleast carbohydrates, such as C5 and/or C6 carbohydrates. In oneembodiment, the pretreated wood based material (1) comprises at least C5carbohydrates. In one embodiment, the pretreated wood based material (1)comprises at least C5 and C6 carbohydrates. Further, in one embodiment,the pretreated wood based material comprises chemical compounds. In oneembodiment, the pretreated wood based material comprises organic acidsand/or other organic compounds. In one embodiment, the pretreated woodbased material comprises furfural. Further, the pretreated wood basedmaterial (1) may comprise also other components, such as side anddegradation products. In one embodiment, the pretreated wood basedmaterial (1) is formed from raw material. In one embodiment, thepretreated wood based material (1) is formed in a wood-to-sugar process.In one embodiment, the raw material comprises at least one of wood basedmaterial, wood, lignocellulosic biomass, agricultural residues, bagassebased material, sugarcane bagasse, corn based material, corn stover,wheat straw, rice straw, woody biomass, woody perennials, vascularplants, recycled brown board or deinking pulp, or their mixtures ortheir combinations. Preferably, the raw material is cellulose basedmaterial. The raw material may comprise lignin, lignocellulose,cellulose, hemicellulose, glucose, xylose and/or extractives. Further,the raw material may comprise other inherent structural components ofbiomass as well as foreign components such as enzymes or chemicals. Inone embodiment, the raw material comprises wood based material or amixture comprising wood based material. In one embodiment, the rawmaterial is wood based material or a mixture comprising wood basedmaterial. In one embodiment, the wood based material is selected fromhardwood, softwood or their combination. In one embodiment, the rawmaterial comprises plant pieces, e.g. wood pieces. In one embodiment,the raw material comprises lignin, cellulose, carbohydrates and somechemical compounds. In one embodiment, the raw material may be treatedby means of any suitable method for forming the pretreated wood basedmaterial (1). In one embodiment, the pretreated wood based material (1)is formed from the raw material which preferably is treated to dissolveat least a part of hemicellulose or a main part of hemicellulose. In oneembodiment, the raw material is pre-treated, preferably by means of asuitable pretreatment stage which may be selected from the groupcomprising physical pretreatment, such as milling, extrusion, microwavepretreatment, ultrasound pretreatment and freeze pretreatment, chemicalpretreatment, such as acid pretreatment, alkaline pretreatment, ionicliquid pretreatment, organosolv pretreatment and ozonolysis,physico-chemical pretreatment, such as steam explosion pretreatment,ammonia fiber explosion pretreatment, CO₂ explosion pretreatment, liquidhot water pretreatment and wet oxidation, biological pretreatment andtheir combinations. In one embodiment, the raw material is treated bythe hydrolysis, e.g. acid hydrolysis, autohydrolysis, thermalhydrolysis, supercritical hydrolysis and/or subcritical hydrolysis, inwhich at least a part of hemicellulose is separated from the rawmaterial in connection with the hydrolysis. In one embodiment, the rawmaterial is treated by a dilute acid hydrolysis or an autohydrolysis. Inone embodiment, the raw material is treated by the hydrolysis and by thesteam explosion in one or more steps. In one embodiment, the rawmaterial is treated by the catalytic pretreatment, e.g. by using acid orbase as catalyst. In the pretreatment stage the raw material enters thereactor unit where the pretreatment takes place. The raw material can betreated by means of one or more pretreatment. The treated raw materialcan be then supplied directly, via an intermediate step, via anadditional treatment step or via an intermediate storage as a pretreatedwood based material (1) to a desired steam treatment stage (2). Further,in one embodiment, the raw material can be dewatered, e.g. by dewateringpresses, and/or washed in one or two or more stages. The dewateringmakes possible to separate sugar based streams.

In this context, a pretreated and steam-treated wood based material (4)means any stream which is formed, e.g. by separating, collecting orrecovering, from a pretreated wood based material (1) in any steamtreatment stage (2) and which comprises at least carbohydrates, such asC5 and/or C6 carbohydrates. In one embodiment, the pretreated andsteam-treated wood based material (4) comprises at least C5carbohydrates. In one embodiment, the pretreated and steam-treated woodbased material (4) comprises at least C5 and C6 carbohydrates. Further,in one embodiment, the pretreated and steam-treated wood based material(4) comprises furfural and/or organic acids. Further, the pretreated andsteam-treated wood based material (4) may comprise also othercomponents, such as side and degradation products. In one embodiment,the pretreated and steam-treated wood based material (4) is a liquidfraction of the pretreated wood based material. Preferably, thepretreated and steam-treated wood based material (4) is formed from thepretreated wood based material after the same steam treatment stage,e.g. a steam explosion stage, than the steam stream (3). Preferably, thepretreated and steam-treated wood based material (4) is in the form ofliquid, e.g. liquid or suspension.

In one embodiment, the pretreated and steam-treated wood based material(4) is diluted in a dilution stage (5) and is treated in a separationstage (6) in which C5 based fraction (7) and C6 based fraction (8) areseparated. C5 based fraction (7) comprises at least C5 carbohydrates. C5based fraction (7) may comprise furfural and/or organic acids. Further,C5 based fraction (7) may comprise also other agents or components.

In one embodiment, the pretreated and steam-treated wood based material(4) or C5 based fraction (7) is supplied to a concentration stage (9)for forming a concentrated carbohydrate based material (11) and thematerial stream (10) which comprises at least furfural. In oneembodiment, temperature of the pretreated and steam-treated wood basedmaterial (4) or C5 based fraction (7) which is supplied to theconcentration stage (9) is below 80° C., preferably below 75° C. Thepretreated and steam-treated wood based material (4) or C5 basedfraction (7) may be treated in one or more than one concentration stage(9). In one embodiment, the concentration stage (9) comprises at leasttwo or more steps, and the material stream (10) is mainly discharged orrecovered from the concentration stage after the first step. Thematerial stream (10) may be in the form of steam or liquid after theconcentration stage (9). In one embodiment, the material stream (10) isa vapor or a condensate of vapor from the concentration stage (9). Inone embodiment, the material stream (10) is a top vapor of theconcentration stage (9). Preferably, furfural accumulates into thematerial stream (10) during the concentration stage (9). In oneembodiment, furfural accumulates mainly into the material stream (10)during the first concentration stage or during the first step of theconcentration stage, and the material stream (10) comprising furfural ismainly collected during the first concentration stage or step. In oneembodiment, apparatus comprises at least one concentration stage (9)which comprises at least one concentration device and in which thepretreated and steam-treated wood based material (4) or C5 basedfraction (7) is concentrated in order to form the concentratedcarbohydrate based material (11) and the material stream (10). In oneembodiment, apparatus comprises more than one concentration stage (9)which comprises at least one concentration device. In one embodiment,apparatus comprises more than one concentration devices. In oneembodiment, apparatus comprises at least one concentration stage (9)which comprises more than one concentration devices. In one embodiment,the concentration stage (9) is an evaporation stage, e.g. a vacuumevaporation, multi-effect evaporation, forced circulation evaporation,film evaporation, or other suitable evaporation or their combinations.In one embodiment, the concentration stage (9) comprises at least oneevaporation device. In one embodiment, the evaporation device isselected from the group comprising a vacuum evaporation device,mechanical vapor compressor, thermal vapor compressor, multi-effectevaporation device, forced circulation evaporation device, filmevaporator, plate type evaporator, tube evaporator, batch evaporator,continuous evaporator and their combinations.

In this context, a material stream (10) means any material stream whichis formed, e.g. by separating, collecting or recovering, from thepretreated and steam-treated wood based material (4) or C5 basedfraction (7). The material stream (10) may comprise furfural and alsoorganic acids, such as acetic acid or other organic acids. In oneembodiment, the material stream comprises at least water, furfural andorganic acids. The material stream may comprise also other components.In one embodiment, the material stream (10) is a fraction of thepretreated and steam-treated wood based material (4) or C5 basedfraction (7). In one embodiment, the material stream (10) comprises afraction of the pretreated and steam-treated wood based material (4) orC5 based fraction (7) and at least a part of steam stream (3). In oneembodiment, the material stream (10) may be formed from the pretreatedand steam-treated wood based material (4) after any suitable treatmentstage. The material stream (10) may be in the form of steam, such asvapor, or liquid, such as condensate.

In this context, the concentrated carbohydrate based material (11)comprises at least C5 carbohydrates. In one embodiment, the concentratedcarbohydrate based material (11) comprises C5 and C6 carbohydrates. Theconcentrated carbohydrate based material (11) may comprise also otheragents or components. In one embodiment, the concentrated carbohydratebased material (11) is further concentrated in a post-evaporation stage.

In one embodiment, the material stream (10) is supplied to the recoverystage (12 b). In one embodiment, a furfural based fraction (14 b) isseparated in the recovery stage (12 b). In one embodiment, a furfuralbased fraction (14 b) is separated from an aqueous phase (15 b).

In one embodiment, the steam stream (3) is supplied to the pretreatedand steam-treated wood based material (4) or to the C5 based fraction(7). In one embodiment, the steam stream (3) is supplied to thepretreated and steam-treated wood based material (4) or to the C5 basedfraction (7) before or during the concentration stage (9). In oneembodiment, volatile components, e.g. furfural and organic acids, areabsorbed into the pretreated and steam-treated wood based material (4)or to the C5 based fraction (7). In one embodiment, the pretreated andsteam-treated wood based material (4) or to the C5 based fraction (7) ispre-heated by means of the steam stream (3) before the concentrationstage (9). Then the energy of the steam stream (3) can be utilized inthe heating.

In one embodiment, the steam stream (3) is supplied to the materialstream (10). In one embodiment, at least a part of the steam stream (3)is supplied to the material stream (10) after the concentration stage(9).

In one embodiment, the steam stream (3) is supplied to the dilutionstage (5).

In one embodiment, the steam stream (3) is cooled or condensed, e.g. bya cooler or condenser, after the steam treatment stage (2), and thecooled steam stream is treated for recovering the furfural basedfraction (14 a,14 b). In one embodiment, the steam stream (3) is cooledor condensed after the steam treatment stage (2), and the cooled steamstream is supplied to the recovery stage (12 a,12 b) in which thefurfural based fraction (14 a,14 b) is separated. In one embodiment, thesteam stream (3) is condensed by water. In one embodiment, the steamstream (3) is supplied to water or aqueous liquid for condensing thesteam stream.

In one embodiment, the steam stream (3) is cooled by means at least oneheat exchanger (13) after the steam treatment stage (2), and the cooledsteam stream is supplied to the recovery stage (12 a) in which thefurfural based fraction (14 a) is separated, and a cooling liquid (16)from the heat exchanger is introduced at least partly to the dilutionstage (5).

In one embodiment, the steam stream (3) is purified by means at leastone scrubber (17) after the steam treatment stage (2) and is supplied toa recovery stage (12 a). In one embodiment, the steam stream (3) ispurified by means at least one scrubber (17) after the steam treatmentstage (2) and is supplied to the dilution stage (5).

In one embodiment, the steam stream (3) or a part of the steam streammay be recirculated as a recirculation flow (24) back to steam treatmentstage (2) for increasing concentration of the steam stream. In oneembodiment, pressure of the recirculation flow (24) is increased, e.g.by means of a compressor, before the steam treatment stage (2). In oneembodiment, the recirculation flow (24) is supplied to a compressor,e.g. a turbo compressor, and from the compressor to the steam treatmentstage (2). The pressure may be increased in one or more steps. In oneembodiment, the recirculation flow (24) is used as an additional steam,e.g. as a booster steam, in the steam treatment stage (2), e.g. in thesteam explosion. By means of the recirculation of the steam streamfurfural concentration may be increased in the steam stream (3).

In one embodiment, the steam stream (3) or a part of the steam streammay be used in a preheating of the pretreated wood based material (1) orin the preheating of the raw material. In one embodiment, the steamstream (3) or a part of the steam stream is supplied to a preheatingstep of the pretreated wood based material (1). In one embodiment, thesteam stream (3) or a part of the steam stream is supplied to apreheating step of the raw material.

In one embodiment, at least a part of C5 based fraction (7) is suppliedto the steam stream (3) or to a mixing stage (18) to which the steamstream (3) is supplied, and the steam stream (3) is condensed by the C5based fraction (7), and the mixture (19) of the steam stream and C5based fraction is supplied to a recovery stage (12 a).

The recovery stage (12 a,12 b) comprises at least one recovery device.The recovery device may be any suitable recovery device. In oneembodiment, the recovery device is a separation device in which thefurfural based fraction (14 a,14 b) is separated from other fractions,e.g. from aqueous phase (15 a,15 b).

In one embodiment, the recovery stage (12 a,12 b) comprises at least oneseparation column and at least one decanter for recovering the furfuralbased fraction (14 a,14 b). In one embodiment, the recovery stage (12a,12 b) comprises at least one separation column for recovering thefurfural based fraction (14 a,14 b). In one embodiment, the recoverystage (12 a,12 b) comprises at least one decanter for recovering thefurfural based fraction (14 a,14 b). In one embodiment, a vaporcondensate, e.g. a top vapor condensate, is formed in the separationcolumn. In one embodiment, the vapor condensate is introduced from theseparation column to the decanter in which two liquid phases, i.e.furfural based fraction (14 a,14 b) and aqueous phase (15 a,15 b), areseparated from each other. In one embodiment, the vapor condensate issupplied out from a suitable part of the separation column, e.g. as amain or side flow. In one embodiment, the vapor condensate is suppliedout from a top part of the separation column. In one embodiment, the topvapor condensate is introduced from a top end of the separation columnto the decanter in which two liquid phases, i.e. furfural based fraction(14 a,14 b) and aqueous phase (15 a,15 b), are separated from eachother. Preferably, in the decanter the vapor condensate or the top vaporcondensate splits in two liquid phases. In one embodiment, the top vaporcondensate is supplied to a bottom part of the decanter. In oneembodiment, the furfural based fraction (14 a,14 b) which comprises atleast furfural is recovered in connection with the decanter. In oneembodiment, the furfural based fraction (14 a,14 b) is recovered from anupper part of the decanter and the aqueous phase (15 a,15 b) isdischarged from the bottom part of the decanter. In one embodiment, theseparation surface of the furfural based fraction and the aqueous phaseis adjusted to a suitable level during the decantation in the decanter.Preferably, the furfural based fraction comprises furfural in highpurity, i.e. the furfural based fraction is a furfural rich phase. Inone embodiment, by means of the ratio of the furfural based fraction andthe aqueous phase and by means of the process conditions can be adjustedthe purity of the furfural based fraction. In one embodiment, theaqueous phase (15 a,15 b) is recirculated to the separation column. Theaqueous phase may comprise water and organic acids, such as acetic acid.Further, in one embodiment, the aqueous phase may comprise alsofurfural. Any suitable device can be used as the recirculating device.In one embodiment, the recirculating device is selected from the groupcomprising assembly, pump, outlet, inlet, pipe, tube, duct, dischargeoutlet, discharge valve, discharge channel, conduit, other suitablefeeding device, other suitable device and their combinations. In oneembodiment, the aqueous phase (15 a,15 b) is supplied as a reflux to theseparation column. Further, in one embodiment, the recovery stage (12a,12 b) comprises at least one device for collecting furfural basedfraction (14 a,14 b).

In connection with the separation column a feed, such as material stream(10), steam stream (3), mixture comprising steam stream (19), condensedstream (21), purified stream (22) or cooled steam stream (23), may beintroduced to any suitable part of the separation column. In oneembodiment, the feed is introduced to the top part of the separationcolumn. In one embodiment, the feed is introduced to the bottom part ofthe separation column. In one embodiment, the feed is introduced to themiddle part of the separation column. In one embodiment, the separationcolumn comprises trays or plates. In one embodiment, the separationcolumn comprises 5-20 stages or trays. In one embodiment, the separationdevice comprises one or more than one columns. In one embodiment thefeed, such as material stream (10), steam stream (3), mixture comprisingsteam stream (19), condensed stream (21), purified stream (22) or cooledsteam stream (23), is introduced to the separation column incounter-current to a vapor formed in the separation column. In oneembodiment, the vapor strips out furfural from the feed leading to anincreased concentration of furfural at the top part or top end of theseparation column. In one embodiment, the aqueous phase (15 a,15 b) issupplied as the reflux to the separation column in counter-current tothe feed.

In one embodiment, the recovery stage (12 a,12 b) comprises a coolingstage which comprises at least one cooling device and in which the topvapor condensate (6) is cooled before the decanter (10). The coolingdevice may be any suitable cooling device, e.g. a heat exchanger orcondenser.

In one embodiment, the separation column is based on a hetero-azeotropicdistillation. In one embodiment, an azeotropic mixture comprises atleast furfural and water. In one embodiment, the separation column is ahetero-azeotropic distillation device. In the hetero-azeotropicdistillation two liquid phases are on the plate. The top vaporcondensate splits in two liquid phases which can be separated in thedecanter. In one embodiment, the top vapor condensate comprises at leastfurfural and water. In one embodiment, the hetero-azeotropicdistillation is a batch distillation process. In one embodiment, thehetero-azeotropic distillation is a continuous distillation process.

In one embodiment, a by-product is discharged out from the separationcolumn. In one embodiment, the by-product is discharged from the bottomend of the separation column. The by-product may comprise water, e.g.washing water or dilution water, and/or organic acids, e.g. acetic acid.In one embodiment, the by-product is a water based stream. In oneembodiment, the by-product is a residue from the distillation.

In one embodiment, at least one carboxylic acid fraction is recovered inthe recovery stage (12 a,12 b). In one embodiment, an acetic acidfraction is recovered in the recovery stage (12 a,12 b). The carboxylicacid fraction may be recovered from the bottom of the separation columnor from any suitable part, such as from a desired tray or plate, of theseparation column.

In one embodiment, the furfural based fraction (14 a,14 b) is purifiedand/or concentrated in at least one furfural purification stagecomprising at least one purification device after the decanter. In oneembodiment, the purification device may be an additional distillationdevice or the second separation column, e.g. hetero-azeotropicdistillation device, or other suitable device.

In one embodiment, the furfural based fraction (14 a,14 b) comprisesfurfural over 70% by weight, preferably over 80% by weight, morepreferably over 90% by weight and most preferably over 95% by weight.

In one embodiment, the method is based on a continuous process. In oneembodiment, the apparatus is a continuous apparatus. In one embodiment,the method is based on a batch process. In one embodiment, at least apart of the apparatus is a batch apparatus.

A furfural based product comprising the furfural based fraction (14 a,14b) may be formed according to any method or apparatus defined above. Inone embodiment, the furfural based product is in the form of liquid.

A chemical product comprising a carboxylic acid fraction may be formedaccording to any method or apparatus defined above. In one embodiment,the chemical product is in the form of liquid.

The furfural based fraction (14 a,14 b) may be used as a source materialin an additional treatment, chemical treatment, polymerization process,manufacture of a chemical, plastic, cellulose acetate or varnish, orother suitable process, or as a component in a fuel or combustionmaterial, or their combinations.

The method and the apparatus provide furfural and also carbohydratestreams with good quality. By means of the method and apparatuscarbohydrate based streams can be purified and waste water treatmentplant loading, and also chemical oxygen demand (COD), can be reduced andvaluable components can be recovered. Further, by means of the methodand apparatus energy recirculation can be improved.

The method and the apparatus provide an industrially applicable, simpleand affordable way of separating and recovering furfural. The method orthe apparatus is easy and simple to realize as a production process. Themethod and the apparatus are suitable for use in connection with themanufacture of the different lignin and carbohydrate products fromdifferent raw materials.

EXAMPLES

Some embodiments of the invention are described in more detail by thefollowing examples with reference to accompanying drawings.

Example 1

In this example, furfural is recovered from a steam stream (3) accordingto a process of FIG. 1 and FIG. 2.

The steam stream (3) is formed in a treatment of a pretreated wood basedmaterial (1). The pretreated wood based material (1) which comprises atleast carbohydrates is treated in a steam treatment stage (2), such asin a steam explosion stage, which comprises at least one steam treatmentdevice, e.g. steam explosion device, and in which the steam is released.The steam stream (3) and pretreated and steam-treated wood basedmaterial (4) are separated in connection with the steam treatment stage(2), for example by means of at least one separation device, e.g.cyclone. The steam stream (3) which comprises furfural is supplied outfrom the steam treatment stage (2) by means of at least one dischargemeans. Also the pretreated and steam-treated wood based material (4)which comprises carbohydrates is supplied out from the steam treatmentstage (2) by means of at least one discharge means. The pretreated woodbased material has been formed from raw material by pretreating the rawmaterial. The raw material is wood based material or a mixturecomprising wood based material. The steam stream (3) is in the form ofsteam, such as water based steam.

According to FIG. 1, the pretreated and steam-treated wood basedmaterial (4) is diluted in a dilution stage (5) and is treated in aseparation stage (6) in which C5 based fraction (7) and C6 basedfraction (8) are separated. C5 based fraction (7) is supplied to aconcentration stage (9) comprising at least one concentration device,e.g. an evaporation device, in which the C5 based fraction isconcentrated in order to form a concentrated carbohydrate based material(11) and the material stream (10) which comprises furfural. The steamstream (3) is supplied into the C5 based fraction (7) before or duringthe concentration stage (9). Alternatively, according to FIG. 2, thepretreated and steam-treated wood based material (4) is supplieddirectly from the steam treatment stage (2) to the concentration stage(9) and the steam stream (3) is supplied into the pretreated andsteam-treated wood based material before or during the concentrationstage (9). In the process according to FIG. 1 or 2, the material stream(10) is collected during the concentration. The material stream may be avapor or a condensate of vapor from the concentration device.

The material stream (10) is treated in at least one recovery stage (12b) for recovering a furfural based fraction (14 b). The material stream(10) is supplied to the recovery stage (12 b) in which the furfuralbased fraction (14 b) is separated from an aqueous phase (15 b).

In this example, the recovery stage (12 b) comprises at least oneseparation column which is based on a hetero-azeotropic distillation andin which at least a top vapor condensate comprising at least furfuraland water is formed, and at least one decanter to which the top vaporcondensate is introduced from a top end of the separation column and inwhich two liquid phases (14 b,15 b) are separated from each other.Further, the recovery stage may comprise a cooling device in which thetop vapor condensate may be cooled before the decanter. Further, therecovery stage comprises at least one recirculating device for supplyingan aqueous phase (15 b) as a reflux from the decanter to the separationcolumn. Carboxylic acid fraction or fractions may be recovered in theseparation column. Further, by-products may be discharged out from theseparation column. The by-product may comprise water and/or organicacids, e.g. acetic acid. Preferably, the material stream (10) isintroduced to the separation column in counter-current to a vapor formedin the separation column. Preferably, the aqueous phase (15 b) issupplied as the reflux to the separation column in counter-current tothe material stream (10).

Further, the furfural based fraction (14 b) may be purified and/orconcentrated in at least one furfural purification stage comprising atleast one purification device after the decanter.

Example 2

In this example, furfural is recovered from a steam stream (3) accordingto a process of FIG. 3.

The steam stream (3) is formed in a treatment of a pretreated wood basedmaterial (1). The pretreated wood based material (1) which comprises atleast carbohydrates is treated in a steam treatment stage (2), such asin a steam explosion stage, which comprises at least one steam treatmentdevice, e.g. steam explosion device, and in which the steam is released.The steam stream (3) and pretreated and steam-treated wood basedmaterial (4) are separated in connection with the steam treatment stage(2), for example by means of at least one separation device, e.g.cyclone. The steam stream (3) which comprises furfural is supplied outfrom the steam treatment stage (2) by means of at least one dischargemeans. Also the pretreated and steam-treated wood based material (4)which comprises carbohydrates is supplied out from the steam treatmentstage (2) by means of at least one discharge means. The pretreated woodbased material has been formed from raw material by pretreating the rawmaterial. The raw material is wood based material or a mixturecomprising wood based material. The steam stream (3) is in the form ofsteam.

The pretreated and steam-treated wood based material (4) can be dilutedin a dilution stage (5) and can be treated in a separation stage (6) inwhich C5 based fraction (7) and C6 based fraction (8) are separated. C5based fraction (7) is supplied to a concentration stage (9) comprisingat least one concentration device, e.g. an evaporation device, in whichthe C5 based fraction is concentrated in order to form a concentratedcarbohydrate based material (11) and the material stream (10) whichcomprises furfural.

The steam stream (3) is supplied to a condensing stage (20) in which thesteam stream (3) is condensed with water. The steam stream or a part ofthe steam stream (24) may be recirculated back to steam treatment stage(2) for increasing concentration of the steam stream. This recirculationmay be carried out also in the processes of the other examples.

The condensed stream (21) is supplied to the recovery stage (12 a) inwhich the furfural based fraction (14 a) is separated from an aqueousphase (15 a). Further, a vapor flow from the condensing stage (20) maybe introduced to the recovery stage (12 a).

In this example, the recovery stage (12 a) comprises at least oneseparation column which is based on a hetero-azeotropic distillation andin which at least a top vapor condensate comprising at least furfuraland water is formed, and at least one decanter to which the top vaporcondensate is introduced from a top end of the separation column and inwhich two liquid phases (14 a,15 a) are separated from each other.Further, the recovery stage may comprise a cooling device in which thetop vapor condensate may be cooled before the decanter. Further, therecovery stage comprises at least one recirculating device for supplyingan aqueous phase (15 a) as a reflux from the decanter to the separationcolumn. Carboxylic acid fraction or fractions may be recovered in theseparation column. Further, by-products may be discharged out from theseparation column. The by-product may comprise water and/or organicacids, e.g. acetic acid. Preferably, the condensed stream (21) isintroduced to the separation column in counter-current to a vapor formedin the separation column. Preferably, the aqueous phase (15 a) issupplied as the reflux to the separation column in counter-current tothe condensed stream (21).

Further, the furfural based fraction (14 a) may be purified and/orconcentrated in at least one furfural purification stage comprising atleast one purification device after the decanter.

Example 3

In this example, furfural is recovered from a steam stream (3) accordingto a process of FIG. 4.

The steam stream (3) is formed in a treatment of a pretreated wood basedmaterial (1). The pretreated wood based material (1) which comprises atleast carbohydrates is treated in a steam treatment stage (2), such asin a steam explosion stage, which comprises at least one steam treatmentdevice, e.g. steam explosion device, and in which the steam is released.The steam stream (3) and pretreated and steam-treated wood basedmaterial (4) are separated in connection with the steam treatment stage(2), for example by means of at least one separation device, e.g.cyclone. The steam stream (3) which comprises furfural is supplied outfrom the steam treatment stage (2) by means of at least one dischargemeans. Also the pretreated and steam-treated wood based material (4)which comprises carbohydrates is supplied out from the steam treatmentstage (2) by means of at least one discharge means. The pretreated woodbased material has been formed from raw material by pretreating the rawmaterial. The raw material is wood based material or a mixturecomprising wood based material. The steam stream (3) is in the form ofsteam, such as water based steam.

The pretreated and steam-treated wood based material (4) is diluted in adilution stage (5) and is treated in a separation stage (6) in which C5based fraction (7) and C6 based fraction (8) are separated. C5 basedfraction (7) is supplied to a concentration stage (9) comprising atleast one concentration device, e.g. an evaporation device, in which theC5 based fraction is concentrated in order to form a concentratedcarbohydrate based material (11) and the material stream (10) whichcomprises furfural.

The steam stream (3) is supplied to a condensing stage (20) in which thesteam stream (3) is condensed with water. The condensed stream (21) issupplied to the dilution stage (5) in which the condensed stream is usedas a dilution liquid. Further, a vapor flow from the condensing stage(20) may be introduced to the concentration stage (9).

The material stream (10) is collected during the concentration. Thematerial stream may be a vapor or a condensate of vapor from theconcentration device. The material stream (10) is treated in at leastone recovery stage (12 b) for recovering a furfural based fraction (14b). The material stream (10) is supplied to the recovery stage (12 b) inwhich the furfural based fraction (14 b) is separated from an aqueousphase (15 b).

In this example, the recovery stage (12 b) comprises at least oneseparation column which is based on a hetero-azeotropic distillation andin which at least a top vapor condensate comprising at least furfuraland water is formed, and at least one decanter to which the top vaporcondensate is introduced from a top end of the separation column and inwhich two liquid phases (14 b,15 b) are separated from each other.Further, the recovery stage may comprise a cooling device in which thetop vapor condensate may be cooled before the decanter. Further, therecovery stage comprises at least one recirculating device for supplyingan aqueous phase (15 b) as a reflux from the decanter to the separationcolumn. Carboxylic acid fraction or fractions may be recovered in theseparation column. Further, by-products may be discharged out from theseparation column. The by-product may comprise water and/or organicacids, e.g. acetic acid. Preferably, the material stream (10) isintroduced to the separation column in counter-current to a vapor formedin the separation column. Preferably, the aqueous phase (15 b) issupplied as the reflux to the separation column in counter-current tothe material stream (10).

Further, the furfural based fraction (14 b) may be purified and/orconcentrated in at least one furfural purification stage comprising atleast one purification device after the decanter.

Example 4

In this example, furfural is recovered from a steam stream (3) accordingto a process of FIG. 5.

The pretreated wood based material (1) and the pretreated andsteam-treated wood based material (4) are treated according to Example 1and FIG. 1. The steam stream (3) is supplied to the dilution stage (5).A mixture of the pretreated and steam-treated wood based material (4)and the steam stream (3) is treated according to Example 1 and FIG. 1for recovering a furfural based fraction (14 b).

Example 5

In this example, furfural is recovered from a steam stream (3) accordingto a process of FIG. 6.

The pretreated wood based material (1) and the pretreated andsteam-treated wood based material (4) are treated according to Example 2and FIG. 3. The steam stream (3) is purified by means at least onescrubber (17) after the steam treatment stage (2), and a purified stream(22) is supplied to a recovery stage (12 a). The purified stream (22) istreated in the recovery stage (12 a) according to Example 2 forrecovering a furfural based fraction (14 a). Further, a vapor flow fromthe scrubber (17) may be introduced to the recovery stage (12 a).

Example 6

In this example, furfural is recovered from a steam stream (3) accordingto a process of FIG. 7.

The pretreated wood based material (1) and the pretreated andsteam-treated wood based material (4) are treated according to Example 3and FIG. 4. The steam stream (3) is purified by means at least onescrubber (17) after the steam treatment stage (2), and a purified stream(22) is supplied to a dilution stage (5) in which the purified stream isused as a dilution liquid. Further, a vapor flow from the scrubber (17)may be introduced to the concentration stage (9). A mixture of thepretreated and steam-treated wood based material (4) and the purifiedstream (22) is treated according to Example 3 and FIG. 4 for recoveringa furfural based fraction (14 b).

Example 7

In this example, furfural is recovered from a steam stream (3) accordingto a process of FIG. 8.

The pretreated wood based material (1) and the pretreated andsteam-treated wood based material (4) are treated according to Example 2and FIG. 3. The steam stream (3) is cooled by means at least one heatexchanger (13) after the steam treatment stage (2). The cooling is madeby water in the heat exchanger. The cooled steam stream (23) is suppliedto a recovery stage (12 a). The cooled steam stream (23) is treated inthe recovery stage (12 a) according to Example 2 for recovering afurfural based fraction (14 a). Further, a vapor flow from the heatexchanger (13) may be introduced to the recovery stage (12 a).

A cooling water (16) from the heat exchanger is introduced at leastpartly to the dilution stage (5) in which the cooling water (16) is usedas a dilution liquid. Further, a material stream (10) may be treated ina recovery stage (12 b) according to Example 1 for recovering a furfuralbased fraction (14 b).

Example 8

In this example, furfural is recovered from a steam stream (3) accordingto a process of FIG. 9.

The pretreated wood based material (1) and the pretreated andsteam-treated wood based material (4) are treated according to Example 2and FIG. 3. At least a part of C5 based fraction (7) is supplied to amixing stage (18). Also the steam stream (3) from the steam treatmentstage (2) is supplied to the mixing stage (18) in which the steam streamand C5 based fraction is mixed. Alternatively, a part of C5 basedfraction (7) can be fed directly to the steam stream (3). The steamstream (3) is condensed by the C5 based fraction (7). The mixture (19)of the steam stream and C5 based fraction is supplied to a recoverystage (12 a). The mixture (19) is treated in the recovery stage (12 a)according to Example 2 for recovering a furfural based fraction (14 a).Further, a vapor flow from the mixing stage (18) may be introduced tothe recovery stage (12 a).

Example 9

In this example material streams (10) of a multistage concentration wasstudied.

A diluted acid pretreated birch based material (1) was treated by meansof a steam treatment stage (2) comprising a steam explosion according tothe process of FIG. 1. A pretreated and steam-treated wood basedmaterial (4) was diluted in a dilution stage (5) and was treated in aseparation stage (6) in which C5 based fraction (7) and C6 basedfraction (8) were separated. C5 based fraction (7) was supplied to aconcentration stage (9) which comprises two steps. The evaporation wasperformed by means of a laboratory scale rotary evaporator in vacuumconditions and at temperature of about 78° C. Samples were collectedfrom vapor and carbohydrate streams of the concentration after eachsteps of the concentration stage.

The C5 based fraction (7) contained carbohydrates, e.g. xylose andglucose, 59 g/l and furfural 4.45 g/l. A concentrated carbohydrate basedflow of sample 1 after the first step contained carbohydrates 100 g/land furfural 0.58 g/l. 1 ^(st) condensate of sample 1 after the firststep contained carbohydrates 0 g/l and furfural 10 g/l. A concentratedcarbohydrate based flow of sample 2 after the second step containedcarbohydrates 363 g/l and furfural 0.04 g/l. 2^(nd) condensate of sample2 after the second step contained carbohydrates 0 g/l and furfural 0.49g/l. The carbohydrate and furfural contents of the C5 based fraction(7), concentrated carbohydrate based materials (11) and 1^(st) and2^(nd) condensates are shown in table 1.

TABLE 1 Carbohydrate Carbohydrate C5 based 1^(st) condensate based basedflow of of flow of 2^(nd) condensate fraction sample 1 sample 1 sample 2of sample 2 Carbohydrates, 59 100 0 363 0 g/l Furfural, 4.45 0.58 100.04 0.49 g/l

It was observed that furfural accumulated mainly into the vapor stream,i.e. 1 st condensate, during the first step of the concentration stage,and therefore the material stream (10) comprising furfural was mainlycollected during the first concentration step.

The method and apparatus according to the present invention is suitablein different embodiments to be used in different furfural recoveryprocesses. Further, the method and apparatus according to the presentinvention is suitable in different embodiments to be used for producingthe most different kinds of carbohydrate fractions and chemical productsfrom different raw materials.

The invention is not limited merely to the example referred to above;instead many variations are possible within the scope of the inventiveidea defined by the claims.

The invention claimed is:
 1. A method for recovering furfural from asteam stream formed in a treatment of a pretreated wood based material,the method comprising: treating the pretreated wood based material,which comprises carbohydrates, in a steam treatment stage in which thesteam stream is released; supplying the steam stream, which comprisesfurfural, out from the steam treatment stage; supplying a pretreated andsteam-treated wood based material, which comprises carbohydrates, outfrom the steam treatment stage; combining the steam stream with at leastone of (a) the pretreated and steam-treated wood based materials, (b) aC5 based fraction separated from the pretreated and steam-treated woodbased material, or (e) a material stream formed from the C5 basedfraction or the pretreated and steam-treated wood based ma al to form aforme stream; and treating the formed stream in a recovery stage forrecovering a furfural based fraction.
 2. The method according to claim1, wherein the steam treatment stage is a steam explosion stage.
 3. Themethod according to claim 1, further comprising: cooling the steamstream after the steam treatment stage and; treating the cooled steamstream for recovering the furfural based fraction.
 4. The methodaccording to claim 1, further comprising: diluting the pretreated andsteam-treated wood based material in a dilution stage; and treating thepretreated and steam-treated wood based material in a separation stagein which a C5 based fraction and a C6 based fraction are separated. 5.The method according to claim 4, further comprising supplying thepretreated and steam-treated wood based material or the C5 basedfraction to a concentration stage for forming a concentratedcarbohydrate based material and a material stream, which comprisesfurfural.
 6. The method according to claim 1, further comprisingsupplying a material stream to the recovery stage.
 7. The methodaccording to claim 1, further comprising: cooling the steam stream afterthe steam treatment stage; and supplying the cooled steam stream to therecovery stage in which the furfural based fraction is separated.
 8. Themethod according to claim 1, further comprising condensing the steamstream by water.
 9. The method according to claim 6, further comprisingsupplying the steam stream to the material stream.
 10. The methodaccording to claim 4, further comprising supplying the steam stream tothe dilution stage.
 11. The method according to claim 4, furthercomprising supplying the steam stream to the pretreated andsteam-treated wood based material or to the C5 based fraction.
 12. Themethod according to claim 1, further comprising: purifying the steamstream using at least one scrubber after the steam treatment stage and;supplying the steam stream to the recovery stage.
 13. The methodaccording to claim 4, further comprising: purifying the steam streamusing at least one scrubber after the steam treatment stage; andsupplying the steam stream to the dilution stage.
 14. The methodaccording to claim 4, further comprising: cooling the steam stream usingat least one heat exchanger after the steam treatment stage; supplyingthe cooled steam stream to the recovery stage in which the furfuralbased fraction is separated; and introducing a cooling liquid from theheat exchanger at least partly to the dilution stage.
 15. The methodaccording to claim 1, further comprising recirculating the steam streamor a part of the steam stream as a recirculation flow back to the steamtreatment stage for increasing concentration of the steam stream. 16.The method according to claim 4, further comprising: supplying at leasta part of the C5 based fraction to the steam stream or to a mixing stageto which the steam stream is supplied; condensing the steam stream bythe C5 based fraction; and supplying the mixture of the steam stream andthe C5 based fraction to the recovery stage.
 17. The method according toclaim 1, wherein the recovery stage comprises at least one separationcolumn and at least one decanter for recovering the furfural basedfraction.
 18. The method according to claim 1, wherein the recoverystage comprises at least one decanter for recovering the furfural basedfraction.
 19. The method according to claim 1, wherein the recoverystage comprises at least one separation column for recovering thefurfural based fraction.
 20. The method according to claim 1, furthercomprising forming the pretreated wood based material from raw material,which is a wood based material or a mixture comprising wood basedmaterial.
 21. An apparatus for recovering furfural from a steam stream,which is formed in a treatment of a pretreated wood based material, theapparatus comprising: at least one a steam treatment stage in which thepretreated wood based material, which comprises at least carbohydrates,is treated and in which the steam is released; at least one dischargemeans for supplying the steam stream, which comprises furfural, out fromthe steam treatment stage; at least one discharge means for supplying apretreated and steam-treated wood based material, which comprisescarbohydrates, out from the steam treatment stage; at least onecombining means for combining the steam stream with at least one of (a)the pretreated and steam-treated wood based material, (b) a C5 basedfraction separated from the pretreated and steam-treated wood basedmaterial, or (c) a material stream formed from the C5 based fraction orthe pretreated and steam-treated wood based material to form a formedsteam stream; and at least one recovery stage for recovering a furfuralbased fraction-from the formed steam stream.